In many filtration systems, filter units are used in a variety of filter housings to clarify influent fluids by allowing them to pass through a filter medium. The filter housings vary in their configurations and can be very deep or very long. Typically, filtration systems employ a modular concept in which a plurality of short filter units are manufactured and then, at the time of installation in the filter housing, connected end to end using an end connector system to form a stack of filter units having the necessary length. An example of a unique end connector system is described in U.S. Pat. No. 5,141,637 to Reed et al. Similarly, a stack of the connected filter units can be installed in the filter housings in the requisite number of rows.
Since the filter housing defines the flow path into and out of the filter units, the stacks of the connected filter units must be properly sealed inside the filter housing in order to prevent influent fluid from bypassing the filter unit to the downstream clean side without first passing through the filter medium. Therefore, filter housings must employ a mechanism for sealing the filter unit prior to fluid clarification.
Two typical sealing mechanisms are the tie rod system and the spring loaded system. Other mechanisms involve the use of elastomeric piston type seal geometries.
In the typical tie rod sealing mechanism, the hollow core of the filter stack is installed over a tie rod in the filter housing. Thereafter, a seal nut is threaded onto the tie rod thereby creating an axial load on filter seals and a fluid-tight connection between the ends of the individual filter units.
Unfortunately, the tie rod system has several disadvantages. Since the tie rod is inserted through the hollow core of the filter stack, the tie rod may interfere with the flow rate through the filter. The tie rod system is also relatively expensive because the tie rod system, which is physically attached to the base of the filter housing, must be designed in conjunction with the filter housing. Furthermore, installation of the tie rod is relatively time consuming.
In the typical spring-loaded sealing mechanism, the connected stacks of filters are installed into the filter housing and a spring-loaded sealing cup is placed on top of the filter stack so that it loosely interfaces with the end of the filter unit. When the housing cover is closed, the spring is compressed thereby providing an axial load onto filter seals and creating a fluid-tight connection between the edges of the sealing cup and the end of the filter unit.
The spring-loaded sealing cup also has several disadvantages. Because the sealing cup loosely interfaces with the filter unit, it is not uncommon for the sealing cup to fall off or otherwise interfere with the handling and installation of the filter stacks in the narrow confines of the filter housing. Additional attention must be given to insure that the sealing cup is properly aligned with the end of the filter unit to maintain seal integrity. Typical sheet metal sealing cups also have non-finished edges that may have burrs or uneven surface edges that can be detrimental to seal integrity.
Since the spring-loaded sealing cup is typically employed to seal string wound or molded depth type filters which require large axial loads to seal the ends of the filter units, the sealing cup is typically a relatively heavy and bulky unit and requires relatively large forces to compress the spring. In many instances, the relatively large forces may cause the filter unit to bow thereby damaging seal integrity.